The model systems analyzed in , reproduced with permission. (a) Mitogen stimulation of thymocyte respiration is depicted as a single open arrow. Respiration is targeted by the mitogen Con A via a number of signal transduction pathways. Analysis of the system should allow one to establish a topology of signal routes and to weight the arrows extending through the signal transduction intermediates (PKC, MAPK, calcineurin and the unidentified pathways). (b) The system depicted in (a) in a modified form. Fewer signal transduction pathways are considered, but their interaction is studied with respect to two blocks of reactions that participate in respiration: the producers and the consumers of the mitochondrial membrane potential (ΔΨm). The responses of these target pathways to Con A via the signal transduction pathways considered can be determined using specific inhibitors of signal transduction (bisindolylmaleimide I and cypermethrin), electron transport (myxothiazol) and ATP synthesis (oligomycin).